The subject of the present invention is aqueous suspensions of inorganic oxidic material which have a lower viscosity than suspensions known heretofore having the same solid-matter content.
It is known that the smaller the individual particles of inorganic fillers or pigments are, the better they can be dispersed in water. In general, comminution of such materials is achieved by mechanical action in an aqueous medium. The fine particles thus obtained, however, have a tendency to reagglomerate. A number of dispersing agents for the prevention of this reagglomeration have already become known.
The known dispersants bring about an increase in the electrokinetic potential; they are adsorbed selectively onto the particles, thereby increasing the charge density on their surfaces. Consequently, those compounds have heretofore been considered as dispersants which have a very large number of negative charges per molecule, an example being tetrasodium pyrophosphate (Na.sub.4 P.sub.2 O.sub.7) as a representative of the inorganic polyanionic compounds, and organic polycarboxylic acids as organic dispersants.
The dispersing action of the polyphosphates for a number of pigments and fillers is just as good as that of the polycarboxylic acids. They have the disadvantage, however, that they decompose during storage as well as when exposed to elevated temperatures.
The polycarboxylic acids known as dispersants are obtained, for example, by the polymerization of acrylic or methacrylic acid or by the saponification of acrylonitrile. In this manner chain-like products are formed, which preferably should contain 18 to 24 carbon atoms per chain.
Whether polycarboxylic acids or polyphosphates are used, the amount of oxidic material that can be incorporated while still maintaining a good working viscosity in the suspension is limited. Known filler or pigment systems having a 70% solids content, such as those desired, for example, by the paper industry, have already a very high viscosity, which makes them difficult to use.
The problem therefore existed of producing aqueous suspensions of good stability having high contents of solid inorganic oxide material, and viscosities decidedly lower than those of the systems known hitherto.